KG-501 is a cAMP response element-binding protein (CREB) inhibitor that disrupts CREB-dependent transcription (Ki = 10 μM) and CREB:CBP interaction (Ki = 50 μM). It also disrupts phospho (Ser-133) CREB binding to KIX with a Ki of ≈90 μM, using concentrations of CREB that were within the linear range of the binding assay.